Method of manufacturing cerium-based polishing agent

ABSTRACT

This invention aims to provide a method of manufacturing a cerium-based abrasive containing coarse particles in lower concentration and having higher polishing ability and excellent cleanability for a polished face. Further, the present invention provides a method of manufacturing a cerium-based abrasive, including the steps of pulverizing a raw material, roasting a raw material after pulverization and disintegrating a raw material after roasting, in which a cerium-based rare earth carbonate or a mixture of a cerium-based rare earth carbonate and a cerium-based rare earth oxide is used as a cerium-based abrasive raw material, and the step of pulverizing a raw material pulverizes a raw material through heating while the material is kept immersed in aqueous solution.

TECHNICAL FIELD

[0001] The present invention relates to a method of manufacturing acerium-based abrasive and more particularly to that method ofmanufacturing a cerium-based abrasive which features a step ofpulverizing a raw material before roasting, and also to a cerium-basedabrasive manufactured by the method thereof.

BACKGROUND ART

[0002] Cerium-based abrasives (hereinafter simply called abrasives) havefrequently been used to polish optical lenses conventionally. Recently,they have also widely been used as abrasives for glass materials used inelectric and electronic apparatuses, including glass for magneticrecording media such as hard disks and glass substrates of liquidcrystal displays (LCD's).

[0003] Cerium-based abrasives are manufactured from, for example,cerium-based rare earth carbonates (hereinafter also called rare earthcarbonates) obtained from bastnasite ores or complex ores produced inChina, or cerium-based rare earth oxides (hereinafter also called rareearth oxides) obtained by calcining rare earth carbonates at hightemperature in advance as follows. First, these raw materials forcerium-based abrasives (hereinafter simply called raw materials) are wetpulverized by a pulverizing apparatus such as an attriter, a ball millor a bead mill, and then are subjected to chemical treatment (wettreatment), followed by filtration and drying. After that, roast byheating appropriately sinters the particles of the raw materials to eachother. The raw material after sintering is dry or wet disintegrated(re-pulverized) using such a pulverizing apparatus as described aboveand then the raw material after disintegration is classified. Suchtreatment provides an abrasive with desired particle diameters and aparticle size distribution. In addition, the chemical treatment in thiscase refers to the treatment (treatment by mineral acids) of removingalkaline metals such as sodium, which give rise to abnormal particlegrowth during roasting, and to the treatment (fluorination) of adding afluorine component for the purpose of attaining the polishing ability ofa cerium-based abrasive and attaining the smoothness of a face to bepolished. A fluorine component reacts with glass, i.e. a material to bepolished, to enhance the smoothness of a face to be polished and thepolishing ability. Therefore, fluorination can offer such effects.

[0004] Incidentally, abrasive products should not contain coarseparticles. This is because coarse particles scratch a face to bepolished. In addition, for example, a polishing step conducted in amanufacturing step for a glass substrate used for a magnetic recordingmedium capable of high density recording and high speed reading andwriting requires a very high degree of precision in the smoothness andthe like of the surface (face to be polished) of a glass substrate.Although these demands need to be satisfied, a high concentration ofcoarse particles in an abrasive is liable to generate scratches on thesurface of a glass substrate; as a result, requirements such assmoothness cannot be attained. Accordingly, in this respect, it isdesirable that an abrasive should not contain coarse particles.

[0005] Furthermore, taking into account polishing operation efficiencyin a polishing step, an abrasive product needs a high polishing ability.Thus, in order to attain a high polishing ability, an abrasive needs tobe pulverized so that the particle diameter is not lowered more thannecessary.

[0006] Incidentally, conventional pulverizing means has some limit, sothat it cannot satisfy these requirements. That is, reduction of thenumber of coarse particles by conventional wet pulverization usingpulverizing apparatuses such as a ball mill, an attriter and a bead millrequires elongated pulverizing duration, which in turn increases theamount of fine particles pulverized more than necessary, leading to thedifficulty of attaining a polishing ability of the abrasive product.

[0007] Hence, conventional abrasives achieve the smoothness required fora face to be polished and polishing ability during polishing by adding afluorine component by fluorination during abrasive production to utilizethe effect of the fluorine component added. As described above, this isdue to the fact that a fluorine component has the effects of enhancingthe smoothness of a face to be polished and of enhancing polishingability. For example, a method is disclosed in Japanese Patent Laid-OpenNo. 9-183966, in which an abrasive is manufactured by droppinghydrofluoric acid aqueous solution, with agitation, into raw materialslurry after wet pulverization so as to make the content of fluorine inan abrasive product become 3% by weight to 9% by weight.

[0008] However, attainment of required smoothness and polishing abilityby the addition of fluorine increases the concentration of the fluorinecomponent in the abrasive, thereby easily adhering the fine particles ofthe abrasive to a face to be polished during polishing and also easilycausing the particles to remain on the face polished, leading to thedisadvantage of lowering cleanability for the face polished.

[0009] The present invention has been made in the background describedabove and offers a subject to provide a method of manufacturing acerium-based abrasive having coarse particles in lower concentration andhaving higher polishing ability and also having excellent cleanabilityfor a polished face.

DISCLOSURE OF THE INVENTION

[0010] In order to solve this subject, the inventors investigatedpulverizing conditions of further decreasing the concentration of coarseparticles and of further decreasing the concentration of fine abrasiveparticles, focusing on the step of pulverizing a raw material in earlystages of abrasive production conventionally carried out by usingpulverizing apparatuses such as an attriter. However, the inventors wereunsuccessful in finding pulverizing conditions under which theconcentrations of both coarse particles and fine abrasive particles canbe further lowered.

[0011] Therefore, the inventors widely studied pulverizing means withoutadhering to conventional pulverizing methods. As a consequence, theinventors have found out that a raw material can be pulverized byheating while the material is kept immersed in aqueous solution when thematerial is special even though it is not pulverized using pulverizingapparatuses such as an attriter, and have arrived at this invention.

[0012] In other words, the present invention is a method ofmanufacturing a cerium-based abrasive, having a step of pulverizing araw material of a cerium-based abrasive and also having a step ofroasting a raw material after pulverization and a step of disintegratinga raw material after roasting, characterized in that a cerium-based rareearth carbonate or a material containing both a cerium-based rare earthcarbonate and a cerium-based rare earth oxide is utilized as a rawmaterial of a cerium-based abrasive, and in that the raw material ispulverized by heating while the material is kept immersed in aqueoussolution in the pulverizing step.

[0013] In the pulverizing step, a cerium-based rare earth carbonate or amaterial containing both a cerium-based rare earth carbonate and acerium-based rare earth oxide is utilized as a raw material and this rawmaterial is pulverized by heating while the material is kept immersed inaqueous solution (hereinafter also called immersion heatingpulverization). The size of a raw material prior to immersion heatingpulverization is not strictly limited; however, a raw material isusually used after the material is coarsely pulverized until the averageparticle diameter becomes 1,000 μm or less, and this level of the sizeis preferable. When the average particle diameter exceeds 1,000 μm, theparticle is preferably ground by a grinder until the average particlediameter becomes 1,000 μm or less before the particle is subjected toimmersion heating pulverization. In addition, a raw material to beimmersed in aqueous solution may be a dried powder or slurry.

[0014] A mixing ratio (ratio by weight) of raw material to aqueoussolution is not particularly limited; however, the weight of aqueoussolution is preferably 0.5 to 10 times that of a raw material (solidcomponent when the raw material is slurry). This is because when theamount of aqueous solution is less than half that of a raw material, theraw material cannot uniformly be heated in some cases, while theuniformity of heating is not improved even when the amount of aqueoussolution is more than 10 times, leading to wastes of heating time andenergy. In addition, aqueous solution used to immerse a raw material iswater itself (pure water, industrial water, tap water, or the like) andalso includes solutions with which water-soluble organic solvents suchas alcohol and acetone are mixed. This is because that these solutionsallow a raw material to be subjected to immersion heating pulverization.

[0015] Aspects of heating while a raw material is kept immersed inaqueous solution include an aspect in which a raw material is immersedin aqueous solution before heated and then the resultant solution isheated, an aspect in which a raw material is immersed in heated aqueoussolution, and an aspect in which a raw material is immersed in heatedaqueous solution and then further heated. In addition, a raw material ispreferably dispersed in aqueous solution by agitation during immersionheating pulverization so as to uniformly heat the raw material.

[0016] When a raw material is pulverized in such a way, the raw material(solid component in slurry) can be pulverized without using aconventional pulverizing apparatus that physically pulverizes a rawmaterial, including an attriter, a ball mill or a bead mill, and furtherthe method can totally pulverize a raw material more uniformly thanconventional pulverizing methods. Additionally, such a conventionalpulverizing method pulverizes a raw material by forcibly movingpulverizing media such as balls, or the like and colliding thepulverizing media with each other, which is liable to form pulverizedand un-pulverized raw materials. As a result, some part of a rawmaterial remains as coarse particles due to a lack of pulverization; onthe other hand, some part is likely to become fine particles due toexcessive pulverization.

[0017] The reason why immersion heating pulverization is possible isthat when a raw material is heated in aqueous solution, some part ofcarbonate in the raw material appears to decompose to release carbondioxide, thereby causing the pulverization to proceed. For example,analysis of a rare earth carbonate after immersion heating pulverizationby an x-ray diffraction apparatus reveals that the monoxycarbonateattributes to the main peak. In addition, immersion heatingpulverization can totally heat a raw material uniformly and reliablythrough the medium of aqueous solution and thus seems to be capable oftotally pulverizing a raw material uniformly. Further, a method ofheating a raw material at a high humidity was considered instead ofimmersion heating; however, the heat conduction is not uniform comparedto the case of immersion heating, thereby leading to less uniformity ofpulverization and to remaining of relatively coarse particles.Additionally, the method needs heating for a long while forpulverization in an extent similar to that of immersion heatingpulverization and therefore causes problems of decreasing productivityand possibly lowering the polishing speed as well. Furthermore,accomplishing the heating at a high humidity requires an expensiveapparatus such as a thermo-hygrostat or a dryer capable of introducingsteam. That is, aqueous solution is excellent as a heating medium foruniformly heating a raw material as compared with steam.

[0018] If a raw material is totally pulverized uniformly, remaining ofcoarse particles is prevented, and partially excessive pulverization isprevented, and the formation of fine particles are also prevented. Inother words, immersion heating pulverization has the effects ofdecreasing the concentrations of both coarse particles and fineparticles in a raw material. If the concentration of coarse particles ina raw material after pulverization can be decreased, the concentrationof coarse particles in an abrasive product can be decreased morereliably and more easily. If the concentration of coarse particles in anabrasive is lowered, the formation of scratches on a face to bepolished, due to coarse particles, is more reliably prevented. Inaddition, if the concentration of fine particles in a raw material afterpulverization can be lowered, the particle diameter of each abrasiveparticle constituting an abrasive consequently becomes near the averageparticle diameter, thereby increasing the polishing speed.

[0019] If a necessary polishing speed is attained, the concentration ofa fluorine component in an abrasive product can be reduced sinceattaining these performances by addition of a fluorine component is notrequired, and so the cleanability for a polished face can be enhanced bylowering the concentration of a fluorine component. Of course, ifnecessary performances such as cleanability are attained, a small amountof fluorine component can be added within an allowable level to thereby,for example, increase the polishing speed. Further, higher levels ofenvironmental measures have recently been required year by year, andtherefore the reduction of the concentration of a fluorine component isthought to be required. If the concentration of a fluorine component canfurther be decreased, the demand can be better satisfied.

[0020] In the step of pulverizing a raw material, immersion heatingpulverization can be carried out along with the pulverization by meansof conventional pulverizing apparatuses such as an attriter, a ball milland a bead mill. Thus, the combination can more effectively performpulverization in some cases. When another pulverizing method is used incombination, immersion heating pulverization may be carried out before,after or concurrently with pulverization by the method.

[0021] In addition, the investigation of immersion heating pulverizationdiscovered that the state of pulverization varies depending on heatingtemperature. Thus, the inventors studied heating temperature. As aresult, it was found out that in the pulverizing step by heating while araw material is kept immersed in aqueous solution, the temperature ofheating the aqueous solution is preferably 60° C. or higher. This isbecause pulverization does not sometimes proceed sufficiently at lowerthan 60° C. On the other hand, the inventors failed to find the upperlimit of the heating temperature. This is because the boiling point ofan aqueous solution in which a raw material is immersed is about 100° C.at normal pressure and heating at a higher temperature needs a specialapparatus such as an autoclave, that is, it is industriallydisadvantageous, and so the inventors did not conduct the experiment.However, the temperature of at least 100° C. or lower can be used topulverize a raw material.

[0022] Further, pulverizing duration for immersion heating pulverizationwas also studied. As a result, in as extremely short a time as 1 minute,immersion heating pulverization was found to pulverize a raw material.In other words, immersion beating pulverization can not only pulverize araw material uniformly, but also rapidly pulverize a raw material in ashort time. However, as the pulverizing duration is elongated, theformation of fine particles caused by excessive pulverization increasesthe concentration thereof, and thus pulverizing duration is preferablyshorter than 90 minutes. Further, to permit the excellent pulverizationof decreasing the concentrations of both coarse particles and fineparticles, the pulverizing duration is more preferably 60 minutes orshorter.

[0023] In addition, as described above, the present invention utilizesas a raw material a cerium-based rare earth carbonate or a materialcontaining both a cerium-based rare earth carbonate and a cerium-basedrare earth oxide. Immersion heating pulverization can pulverize a rawmaterial so as to cause the residual amount of coarse particles and theamount of fine particles generated to be minimized. This seems to bemainly due to its effect on the rare earth carbonate.

[0024] Furthermore, “cerium-based rare earth species” refer to materialsin which the percentage of the amount of cerium oxide (CeO₂) in thetotal amount of rare earth oxides in the total weight (hereinaftercalled TREO) is 30% or more by weight. In normal abrasive production, amaterial in which the percentage ranges from 40% by weight to 99% byweight is utilized. Additionally, a “cerium-based rare earth carbonate”is a material that is obtained using a precipitant containing acarbonate from a “cerium-based rare earth” aqueous solution. Forexample, cerium-based rare earth aqueous solutions include a rare earthchloride aqueous solution and precipitants include ammoniumhydrogencarbonate. In addition, a “cerium-based rare earth oxide” is amaterial made by roasting a cerium-based rare earth carbonate foroxidation.

[0025] Now, a preferable range as a raw material utilized in a method ofmanufacturing a cerium-based abrasive of the present invention wasstudied, focusing on the physical property of loss on ignition(hereinafter also called LOI) for a raw material used for a cerium-basedabrasive. LOI refers to a weight loss rate when a target material isstrongly heated. This value is about 30% by weight to 40% by weight forrare earth carbonates; it is 0% by weight for a completely oxidized rareearth oxide. LOI indicates the proportion of a rare earth carbonate,which is highly chemically pulverized, in a raw material.

[0026] Studies on raw materials containing both a cerium-based rareearth carbonate and a cerium-based rare earth oxide showed that a rawmaterial used for a cerium-based abrasive, having a value of loss onignition of 1.0% by weight to 40% by weight when the raw material washeated at 1,000° C. for 1 hour, is preferable. As the value of LOIbecomes smaller than 1.0% by weight, that is, the percentage of a rareearth carbonate is decreased, the effect of pulverizing coarse particlesappears to be rarely obtainable during pulverization. In addition, amaterial with LOI of less than 0.5% by weight is referred to as a rareearth oxide.

[0027] The measurement of LOI of raw materials was carried out inaccordance with JIS-K0067 (1992, Japanese Standards Association). Themeasurement procedure will be simply described as follows. First, asmall amount of raw material was sampled and it was preliminarily driedat 105° C. sufficiently until no decrease in the amount was observed(for example, for 1 hour). After preliminary drying, in a crucible witha predetermined weight (A g (grams)) was placed the dried raw materialand then the whole weight (B g) was measured to 0.1 mg to evaluate theweight W1 (=B−A) of the raw material. Then, the crucible was heated inan electric furnace at 1,000° C. for 1 hour and then was allowed to coolin a dry atmosphere. Again, the weight (C g) of the crucible containingthe raw material was measured and the difference W2 (=B−C) of theweights before and after the heating was calculated. On the basis ofthis value, LOI (=(W2/W1)×100, unit: % by weight) was evaluated. Inaddition, the reason why preliminary drying is carried out in the LOImeasurement is that a normal raw material contains moisture in manycases and the measurement of LOI, with moisture contained, cannotprovide a useful index that indicates the exact percentage of rare earthcarbonates in a raw material. Further, setting of the preliminary dryingtemperature to be 105° C. is based on JIS-K-0068 (1992), “A Method ofMeasuring Moisture in Chemical Products,” “5. Drying Weight ReductionMethod,” which specifies that a sample shall be heated for drying at105° C. until the weight reaches a constant value. Furthermore, thereason why the weight was measured after a material was heated at 1,000°C. for 1 hour is that for rare earth carbonates, it is experimentallyconfirmed that the value of loss on ignition starts to stabilize byheating at 500° C. or higher, and the index obtained at 1,000° C. isconsidered to be the most stably applicable.

[0028] Incidentally, a raw material containing both a cerium-based rareearth carbonate and a cerium-based rare earth oxide is roughlyclassified into a raw material (former) obtained by calcining acerium-based rare earth carbonate and a raw material (latter) obtainedby mixing a cerium-based rare earth carbonate and a cerium-based rareearth oxide. The former raw material is more excellent in pulverability,and so the concentration of coarse particles in the obtained abrasiveproduct is lower and the raw material is more preferable. The former rawmaterial is obtained by appropriately calcining the whole of a rareearth carbonate raw material and immersion heating pulverization isconsidered to uniformly proceed in the whole raw material due to thefact that the carbonate is uniformly contained in the whole raw materialeven from a relatively microscopic viewpoint. On the other hand, thelatter raw material is a mixture of particles of rare earth carbonateseasy to be pulverized and particles of rare earth oxides hard to bepulverized due to no carbonates contained, and thus it is consideredhard to be pulverized uniformly and coarse particles tend to remain.

[0029] After completion of the step of pulverizing a raw material, astep similar to a normal manufacturing step as described in the priorart is carried out to manufacture an abrasive. More specifically,firstly, a material is subjected to a chemical treatment (wet treatment)as necessary, followed by filtration and drying. Then, the material isroasted to be disintegrated (re-pulverized). When the material isdisintegrated through wet pulverization, decreasing the number of coarseparticles through sufficient disintegration provides an abrasive of aslurry state at the time of completion and further drying the resultantmaterial gives a powder-like abrasive. In some cases, afterdisintegration, the number of the coarse particles and/or fine particlesis decreased through wet classification, or the number of coarseparticles is passed through a cartridge filter to be decreased, or asimilar operation is carried out, to further provide an abrasive of highquality. On the other hand, when disintegration is carried out throughdry pulverization, after disintegration, dry classification is normallyconducted to obtain a powdered abrasive with a desired particle diameterand a particle size distribution. In this case, to obtain an abrasive ofa slurry state, a dry-classified, powdered abrasive may be made slurry,or an abrasive after disintegration through dry pulverization may bemade slurry, and then the slurry is subjected to wet classification.Further, the chemical treatment in this case refers to fluorination ortreatment by mineral acid, and as can be seen from the descriptions thusfar, a method of manufacturing a cerium-based abrasive according to thepresent invention does not necessarily require fluorination, andtherefore a large reduction of the amount of fluorine component added byfluorination and further the reduction to the zero (0) content arepossible.

[0030] As has been described thus far, the method of manufacturing anabrasive of the present invention can pulverize a raw material in such away that the concentrations of both coarse particles and fine particlesare decreased, and thus an abrasive with coarse particles and fineparticles both in low concentrations can be easily manufactured. Thatis, a conventional manufacturing method cannot pulverize a raw materialso as to lower both the concentrations, and so, conventionally, a rawmaterial is, at first, pulverized to lower the concentration of coarseparticles and a necessary polishing ability (polishing speed) isobtained by the addition of a fluorine component. Therefore, it isdifficult to manufacture an abrasive with coarse particles and fluorineboth in low concentrations. On the other hand, a method of manufacturinga cerium-based abrasive according to the present invention can easilyproduce an abrasive excellent in polishing speed, smoothness for a faceto be polished and cleanability, even though the fluorine content in anabrasive is greatly decreased compared with the conventional case, or nofluorine is added. As a result of investigation, of abrasives producedthrough a method of manufacturing a cerium-based abrasive according tothe present invention, an abrasive having a fluorine component in aconcentration of 3.0% or less by weight has been found to be a oneexcellent in smoothness and cleanability for a polished face, as well aspolishing ability, which rarely makes scratches during polishing. Thisis because the cleanability is rapidly decreased when the concentrationof a fluorine component in an abrasive exceeds 3.0% by weight. Further,an abrasive having a fluorine component in a concentration of 0.01% byweight to 1.0% by weight has been found to be particularly excellent incleanability.

BEST MODE FOR CARRYING OUT THE INVENTION

[0031] Best modes for carrying out the present invention will bedescribed in the following.

[0032] First Embodiment: A rare earth carbonate having 12% by weight ofloss on drying, containing 69% by weight of TREO with respect to theweight of a dried material, 60% by weight of cerium oxide (CeO₂) in TREOand 0.1% by weight of a fluorine component with respect to TREO was usedas the cerium-based abrasive raw material. In addition, the averageparticle diameter of the raw material was about 500 μm and the LOI ofthe raw material was 30% by weight. A method of measuring LOI wasdescribed above, and thus its description is omitted. Each Embodiment orComparative Example as described later utilized this raw material,unless otherwise mentioned.

[0033] First, 9.3 kg of pure water was put in the container of aagitating apparatus and was heated to 65° C., and then to this wascharged 5.7 kg of the raw material (of it, water is 0.7 kg) withagitation for 5 minutes. Further, means for heating the water in thecontainer was placed in the agitating apparatus and the slurry in thecontainer was heated from the start time of charging the raw materialuntil the completion of agitation so that the temperature of the slurryin the agitating apparatus was kept at 60° C. or hither (65° C. or lower(=the lower limit temperature+5° C. or lower)). After the completion ofagitation, the slurry (the content of solid component of 33.3% byweight) composed of water and the raw material in the agitatingapparatus was charged into an attriter having 10 kg of balls 4 mm indiameter (MA-1SE, manufactured by Mitsui Miike Machinery Co., Ltd.) andthen was wet pulverized for 1 hour. After pulverization, the solidcomponent was filtered to obtain cake, which was dried and roasted (850°C., 5 hours) and then was disintegrated with a sample mill (manufacturedby Fuji Paudal Co., Ltd.). In order to decrease the number of coarseparticles, the material thus obtained was classified once (classifyingpoint: 7 μm) using a turboplex (manufactured by Hosokawa MicronCorporation), a type of a wind classifying apparatus, to thereby obtaina cerium-based abrasive product. Then, the cerium-based abrasive thusobtained was subjected to the measurement of the particle sizedistribution via a particle size analyzer (Micro-track MK-II SPA MODEL7997-20, manufactured by Nikkiso Co., Ltd.) and then the value of theparticle diameter (average particle diameter (D50)) was evaluated sothat the volume accumulated particle size distribution frequency fromthe small particle diameter side became 50%.

[0034] Measurement of the concentration of coarse particles: In theEmbodiments and Comparative Examples as described later, including theFirst Embodiment, the concentrations of coarse particles (theconcentration of particles with a diameter of 10 μm or more) of the rawmaterial and abrasive products were measured in the specified time ofthe pulverizing step (see Table 1) and the concentrations of coarseparticles for the obtained abrasives were also measured. Theconcentration of coarse particles was measured in the following way. Atarget to be measured was sampled and measured so that the weight of thesolid component of the target was 200 g, and the sample was dispersed inan aqueous solution containing 0.1% by weight of sodiumhexametaphosphate as a dispersant with agitation for 2 minutes tothereby produce slurry. This slurry was filtered using a microsieve witha pore diameter of 10 μm and then the residue on the sieve wascollected. The residue thus collected was again dispersed in a solutionwith 0.1% by weight of sodium hexametaphosphate to be made slurry. Inthis case, dispersion was carried out by means of ultrasonic agitationfor 1 minute. Then, the slurry was filtered using a microsieve with apore diameter of 10 μm. The residue collected was made slurry again andfiltration was conduction twice to collect coarse particles. And then,these coarse particles were sufficiently dried and were measured. Theconcentration of coarse particles was evaluated from the weight of thesecoarse particles.

[0035] Second to Sixth Embodiments and Comparative Examples 1 and 2:Immersion heating pulverization was carried out through varying thewater temperature in the agitating apparatus at the time of charging theraw material and the immersion duration after charging the raw material.The other conditions for manufacturing an abrasive were the same as thecase of First Embodiment, and so the descriptions are omitted.

[0036] Comparative Example 3: The raw material was pulverized onlythrough wet pulverization by means of an attriter in the step ofpulverizing the raw material and roasted without carrying out immersionheating pulverization through an agitating apparatus. More specifically,first, the raw material was mixed with pure water to prepare slurry (thecontent of solid component of 33.3% by weight), and the slurry thusobtained was charged into an attriter and then pulverization wascompleted only by carrying out wet pulverization for 10 hours. The otherconditions for manufacturing an abrasive were the same as the case ofSecond Embodiment. TABLE 1 Concentration of coarse particles (ppm byweight) Raw material Immersion heating pulverization Raw material afterEmbodiment/ Heating Immersion after pulverization Comparativetemperature duration immersion through Example (° C.) (min) heatingattriter Abrasive Comparative 40 5 30000  1200  3300  Example 1 First 605 250 100 430 Embodiment Second 80 5 200 80 270 Embodiment Third 95 1330 140 470 Embodiment Fourth 95 5 150  60 200 Embodiment Fifth 80 20 100  40 150 Embodiment Sixth 80 60   70  20  80 Embodiment Comparative80 180   20 <10 <10 Example 2 Comparative — — — 200 500 Example 3

[0037] Common data for the first raw material:

[0038] LOI=30% by weight

[0039] TREO/raw material=69% by weight

[0040] CeO₂/REO=60% by weight

[0041] In Comparative Example 3, the raw material was pulverized onlythrough pulverization by means of an attriter without carrying outimmersion heating pulverization; it took 10 hours to make theconcentration of the coarse particles of the raw material afterpulverization reach the value indicated in the table. On the other hand,in First Embodiment and Second Embodiment, the raw material wassubjected to immersion heating pulverization for 5 minutes, followed bypulverization by means of an attriter for 1 hour, and after thepulverization, a raw material with a lower concentration of coarseparticles was obtained. As a result, it has been found out thatimmersion heating pulverization permits a raw material to be pulverizedin a shorter time. In addition, it has also been found out that theconcentration of coarse particles in an abrasive product finallyobtained is restrained compared with the case of Comparative Example 3,and that immersion heating pulverization has the effect of lowering theconcentration of coarse particles in an abrasive.

[0042] Comparative Example 1 carried out immersion heatingpulverization, with the temperature of the slurry kept at 40° C. orhigher (45° C. or lower); the concentration of coarse particles in theraw material obtained after immersion heating pulverization was high. Onthe other hand, First Embodiment, in which the concentration of coarseparticles was low, carried out immersion heating pulverization, with thetemperature of the slurry kept at 60° C. or higher (65° C. or lower).This result has shown that for immersion heating pulverization thetemperature of the slurry was preferably kept at 60° C. or higher. Onthe other hand, as for the upper limit of the keeping temperature ofslurry, since Fourth Embodiment, in which the slurry kept at 95° C. orhigher and 100° C. or lower was subjected to immersion heatingpulverization, gave a good pulverization result, it has been shown thatif the keeping temperature of slurry during immersion heatingpulverization is at least at 100° C. or lower, good pulverization thatgives a low concentration of coarse particles can be carried out and theconcentration of coarse particles in the abrasive product is lowered aswell.

[0043] In addition, the results of the Third Embodiment have shown thatif immersion duration is 1 minute or longer, only immersion heatingpulverization can lower the concentration of coarse particles to a levelthat is comparable to the case where only pulverization by means of anattriter was carried out for 10 hours (Comparative Example 3). Further,the concentration of coarse particles in the abrasive product finallyobtained was low as well. On the other hand, as for the upper limit ofimmersion duration the results of Sixth Embodiment and ComparativeExample 2 have shown that as immersion duration is elongated, theconcentration of coarse particles can be decreased.

[0044] Seventh Embodiment: In this Embodiment, the raw material waspulverized only through immersion heating pulverization using anagitating apparatus without carrying out wet pulverization by means ofan attriter. In the immersion heating pulverization, the slurry in thecontainer was heated so as to maintain the temperature of the slurry inthe agitating apparatus at 95° C. or higher (100° C. or lower). Inaddition, the immersion duration was 20 minutes. The otherabrasive-manufacturing conditions were the same as those in SecondEmbodiment.

[0045] Eighth Embodiment: In the step of pulverizing the raw material ofthis Embodiment, at first, the raw material was mixed with pure water toprepare slurry (the content of solid component of 33.3% by weight) andthen the slurry thus prepared was wet pulverized in an attriter. Afterthis wet pulverization, the raw material was charged into an agitatingapparatus to carry out immersion heating pulverization. Except theabrasive-manufacturing condition of firstly carrying out pulverizationby means of an attriter and then carrying out immersion heatingpulverization, the other conditions were the same as the case of SecondEmbodiment, including the keeping temperature for the slurry and theimmersion duration. TABLE 2 Concentration of coarse particles (ppm byweight) Raw material after firstly Raw Immersion heating carrying outRaw material pulverization pulverization material after Embodiment/Heating Immersion by after pulverization Comparative temperatureduration means of immersion by means Example (° C.) (min) attriterheating of attriter Abrasive Second 80 5 — 200 80 270 Embodiment Fourth95 5 — 150 60 200 Embodiment Seventh 95 20  — 120 — 450 EmbodimentEighth 80 5 5000  75 — 220 Embodiment

[0046] Common data for the first raw material:

[0047] LOI=30% by weight

[0048] TREO/raw material=69% by weight

[0049] CeO₂/TREO=60% by weight

[0050] As has already been described, the concentration of coarseparticles can be decreased through immersion heating pulverization.Seventh Embodiment has confirmed that roasting after immersion heatingpulverization without actually carrying out pulverization by means of anapparatus such as an attriter can also provide an abrasive product withcoarse particles in low concentration. In addition, Eighth Embodimenthas shown that a combination of immersion heating pulverization andpulverization by means of an attriter can also give a good pulverizationresult with coarse particles in low concentration even though either ofthe pulverizing methods is carried out first.

[0051] Ninth to Eleventh Embodiments and Comparative Example 4: Fivekilograms of the raw material prepared through calcining the rawmaterial used in First Embodiment (rare earth carbonate) under specifiedcalcining conditions and by adjusting the LOI was charged into 10 kg ofpure water heated in the container of an agitating apparatus and thenthe immersion heating pulverization was carried out. Table 3 givescalcining conditions for each Embodiment and a Comparative Example. Theother abrasive-manufacturing conditions were the same as the case ofSecond Embodiment. TABLE 3 Concentration of coarse particles (ppm byweight) Raw material Immersion heating Raw after pulverization materialpulverization Embodiment/ Calcination Heating Immersion after byComparative Temperature Duration LOI (% by temperature durationimmersion means of Example (° C.) (h) weight) (° C.) (min) heatingattriter Abrasive Second — — 30 80 5 200  80 270 Embodiment Ninth 400 210 80 5 240 100 380 Embodiment Tenth 500 2 5 80 5 290 120 430 EmbodimentEleventh 850 5 1.0 80 5 350 150 500 Embodiment Comparative 950 5 0.5 805 12000  700 1800  Example 4

[0052] In Comparative Example 4, in which the LOI was 0.5% by weight,the concentration of coarse particles in the raw material afterimmersion heating pulverization was extremely high. On the other hand,each Embodiment, in which the LOI was 1.0% by weight or more (40% byweight or less), has shown that the concentrations of coarse particlesin the raw material and an abrasive product after immersion heatingpulverization are kept low. These results have proved that immersionheating pulverization is a particularly effective method ofpulverization, such as being able to reduce the concentration of coarseparticles and also decrease the pulverizing duration, when a rawmaterial for a cerium-based abrasive is a cerium-based rare earthcarbonate or a material containing both a cerium-based rare earthcarbonate and a cerium-based rare earth oxide.

[0053] Twelfth and Thirteenth Embodiments and Comparative Example 5: Theraw material obtained through carrying out immersion heatingpulverization and then carrying out wet pulverization by means of anattriter was subjected to fluorination, followed by roasting. The otherabrasive-manufacturing conditions were the same as the case of SecondEmbodiment. In addition, fluorination was carried out by the addition ofa hydrogen fluoride (HF) aqueous solution to slurry. Other solutions,e.g. ammonium fluoride can be used for the addition to the slurry. Theconcentrations of the fluorine component in raw materials obtainedthrough fluorination are given in Table 4. TABLE 4 Concentration ofConcentration of coarse particles fluorine (ppm by weight) component Rawmaterial Immersion heating of raw 3Raw after pulverization materialmaterial pulverization Embodiment/ Heating Immersion after after byComparative temperature duration fluorination immersion means of Example(° C.) (min) (wt %) heating attriter Abrasive Second 80 5 <0.1  240 100 380 Embodiment Twelfth 80 5 1.0 200 80 270 Embodiment Thirteenth 80 53.0 200 80 250 Embodiment Comparative 80 5 6.0 200 80 200 Example 5

[0054] Common data for the first raw material:

[0055] LOI=30% by weight

[0056] TREO/raw material=69% by weight

[0057] CeO₂/TREO=60% by weight

[0058] The table shows that good pulverized materials with coarseparticles in lowered concentration are obtained even when fluorinationwas carried out after pulverization. However, the comparison with SecondEmbodiment indicates that raw materials and abrasive products afterimmersion heating pulverization are not so different in theconcentration of coarse particles.

[0059] Polishing Test: A cerium-based abrasive in the form of slurry,obtained in each Embodiment or Comparative Example, was subjected topolishing test to thereby measure the polishing value and evaluate thestate of the polished face (evaluate scratches). In the polishing test,a piece of glass of 65 mmφ for a flat panel as a material to be polishedwas polished under a high speed polishing test apparatus using apolishing pad of polyurethane. In the polishing test, an abrasiveobtained was further dispersed in water to prepare abrasive slurry of aconcentration of 10% by weight. The polishing conditions were asfollows: the abrasive slurry obtained was fed at a speed of 5 L/min, thepressure on a face to be polished was set to be 1.54 MPa (15.7 kg/cm²)and the rotational speed of the polishing apparatus was set to be 1,000rpm. A glass material after polishing was cleaned with pure water anddried under dust-free conditions.

[0060] Evaluation of polishing value: In the aforementioned polishingtest, the polishing value was obtained on the basis of the difference ofthe glass weights through measuring the glass weights before and afterpolishing. In this case, the polishing value of the case where theabrasive in Comparative Example 1 was used for polishing was set to be areference (100).

[0061] Evaluation of Scratches: This refers to the evaluation of thestate of a polished face. The evaluation of scratches was conductedbased on the presence or absence of scratches on a polished face. Morespecifically, light of a halogen lamp with a 300,000-lux light sourcewas irradiated to the surface of glass after polishing. The surface ofthe glass was observed through the reflection method and the extent ofscratches (size and number) was judged and rated, and evaluated bydeducting points from one hundred.

[0062] Evaluation of cleanability: The cleanability test of abrasiveswas carried out through cleaning faces polished with the use ofcerium-based abrasives obtained in each Embodiment and each ComparativeExample. A glass plate for optical microscopic observation was subjectedto ultrasonic cleaning and drying for the test. A cerium-based abrasivewas dispersed in water to obtain abrasive slurry of a concentration of10% by weight. The plate was immersed in this abrasive slurry, thenremoved and sufficiently dried in a dryer to obtain a specimen forcleanability test with the abrasive stuck to the surface of the plate.Further, the plate was dried at a temperature of 50° C. Then, thespecimen thus obtained was immersed in pure water in a beaker and wassubjected to ultrasonic cleaning for 5 minutes. After cleaning, theplate was taken out of the beaker and then was put in pure water forflowing water cleaning. The surface of the plate after flowing watercleaning was observed under an optical microscope to evaluate the amountof the residue of the abrasive particles remaining on the surface. Theevaluation results are shown in Table 5. TABLE 5 Abrasive ConcentrationLOI of Immersion heating of raw pulverization Average coarse FluorineEmbodiment/ material Heating Immersion particle particles concentrationEvalution of abrasive Comparative (% by temperature duration diameter(ppm by (% by Polishing Example weight) (° C.) (min) (μm) weight)weight) value Scratches *Cleanability Comparative 30 40 5 1.0 3300  0.03100 35 F Example 1 First 30 60 5 1.0 430 0.02 137 91 E Embodiment Second30 80 5 1.0 270 0.02 129 96 E Embodiment Third 30 95 1 1.1 470 0.02 14090 E Embodiment Fourth 30 95 5 0.9 200 0.01 122 98 E Embodiment Fifth 3080 20  0.9 150 0.02 117 98 E Embodiment Sixth 30 80 60  0.9  80 0.01 11199 E Embodiment Comparative 30 80 180  0.8 <10 0.01  71 95 P Example 2Comparative 30 — — 1.0 500 0.03  70 96 P Example 3 Seventh 30 95 20  1.0450 0.01 122 90 E Embodiment Eighth 30 80 5 1.0 220 0.02 130 96 EEmbodiment Ninth 10 80 5 1.0 380 0.02 135 94 E Embodiment Tenth 5 80 51.0 430 0.01 139 93 E Embodiment Eleventh 1.0 80 5 1.0 500 <0.01 145 90G Embodiment Comparative 0.5 80 5 1.3 1800  <0.01 150 73 F Example 4Twelfth 30 80 5 1.2 270 0.90 152 93 E Embodiment Thirteenth 30 80 5 1.2250 2.60 172 90 G Embodiment Comparative 30 80 5 1.5 200 5.30 195 85 PExample 5

[0063] The polishing test results of the abrasives in ComparativeExample 1 and First to Sixth Embodiments show that abrasives with coarseparticles in low concentration exhibit high evaluations and that theconditions for suitably carrying out immersion heating pulverization arebasically equivalent to those for obtaining an abrasive excellent ineach performance. However, although the abrasive of Comparative Example2 (immersion duration is 180 minutes) is extremely low in theconcentration of coarse particles, the polishing value and cleanabilityare relatively inferior. These results show that if the immersionduration during immersion heating pulverization is made too long, theconcentration of coarse particles is decreased; however, the polishingvalue and cleanability of the abrasive product are lowered. In otherwords, it is shown that in order to obtain an abrasive excellent in allthe evaluations, in addition to the conditions of immersion heatingpulverization described previously, the immersion duration is preferably90 minutes or shorter, and that from the results of Sixth Embodiment,the immersion duration is preferably 60 minutes or shorter. Thus, whenthe immersion duration is likely to exceed 60 minutes, particularly 90minutes, the slurry is preferably once cooled to below 60° C. or lower(preferably ambient temperature). In summary, the keeping temperature ofslurry is preferably in a range of 60° C. to 100° C. and the immersionduration is 1 minute to 90 minutes, particularly preferably 1 minute to60 minutes.

[0064] The test results of the abrasive in Seventh Embodiment are allgood. This Embodiment did not carry out pulverization by means of anattriter. Hence, pulverization of a raw material only through immersionheating pulverization is found to give an excellent abrasive.

[0065] In addition, the test results of the abrasive in EighthEmbodiment are good in all the attributes. In this Embodiment,pulverization by means of an attriter was conducted first, and thenimmersion heating pulverization was carried out. Therefore, alsoreferring to the results of Second Embodiment, in which immersionheating pulverization was carried out first, either immersion heatingpulverization or pulverization by means of an attriter can be carriedout first.

[0066] Referring to the polishing test results of the abrasives of Ninthto Eleventh Embodiments and Comparative Example 4, the concentration ofcoarse particles of a raw material obtained through pulverization ishigh when the LOI of a raw material is low, and the scratch evaluationof an abrasive finally obtained is also low (Comparative Example 4).Further, the concentration of coarse particles of a raw materialobtained through pulverization is low when the LOI of a raw material ishigh, and the evaluations of an abrasive finally obtained is also high.As a result, when a raw material is pulverized through immersion heatingpulverization, a raw material is preferably a cerium-based rare earthcarbonate or a material containing both a cerium-based rare earthcarbonate and a cerium-based rare earth oxide. Thus, such a raw materialcan be pulverized into a good form in a short time, which can lead tothe production of an abrasive excellent in each performance.

[0067] For the abrasives of Twelfth and Thirteenth Embodiments andComparative Example 5, in which fluorination is carried out prior toroasting after pulverization, the concentrations of the coarse particlesof a raw material and an abrasive product after immersion heatingpulverization are comparable to that of Second Embodiment. However, theabrasive of Comparative Example 5, in which the amount of fluorinecomponent added by fluorination is the largest, is inferior in theevaluations of scratches and cleanability. As a result, fluorination isallowable; however, in this case, a large amount of fluorine componentshould not preferably be added. More specifically, the table shows thatthe concentration of the fluorine component of an abrasive is preferablylower than 3.0% by weight, more preferably 1.0% by weight or less.

INDUSTRIAL APPLICABILITY

[0068] The present invention can provide a method of manufacturing acerium-based abrasive having coarse particles in lower concentration, ahigher polishing ability and also being excellent in cleanability for apolished face. In addition, use of the present invention makes itpossible to effectively pulverize a raw material in a short time so asto reliably decrease the concentration of coarse particles and toeffectively produce a cerium-based abrasive having an excellentpolishing ability.

1. A method of manufacturing a cerium-based abrasive comprising thesteps of: pulverizing a raw material of a serium-based abrasive;roasting a raw material after pulverization; and disintegrating a rawmaterial after roasting, wherein a cerium-based rare earth carbonate ora mixture of a cerium-based rare earth carbonate and a cerium-based rareearth oxide is used as a cerium-based abrasive raw material, and thestep of pulverizing a raw material comprises a step of pulverizationthrough heating a raw material kept immersed in aqueous solution.
 2. Themethod of manufacturing a cerium-based abrasive according to claim 1,wherein in the step of pulverization through heating a raw material keptimmersed in aqueous solution, the heating temperature of the aqueoussolution is 60° C. to 100° C.
 3. The method of manufacturing acerium-based abrasive according to claim 1 or 2, wherein the loss onignition for a cerium-based abrasive raw material is 1.0% by weight to40% by weight when the raw material is heated at 1,000° C. for 1 hour.4. A cerium-based abrasive produced by the method of manufacturing acerium-based abrasive according to any one of claims 1 to 3, wherein theconcentration of a fluorine component is 3.0% by weight or less.
 5. Acerium-based abrasive according to claim 4, wherein the concentration ofa fluorine component is 0.01% by weight to 1.0% by weight.